Catalytic device for stoichiometric air-fuel ratio gasoline engine and catalytic system including the same

ABSTRACT

The present disclosure provides a catalytic device for a stoichiometric air-fuel ratio gasoline engine, in which exhaust gas discharged from a gasoline engine sequentially passes through a WCC (Warm up Catalytic Converter) and a UCC (Under floor Catalytic Converter). In particular, the catalytic device may include an LNT (Lean NOx Trap) component added to one of the WCC and the UCC.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2016-0032139, filed on Mar. 17, 2016, which is incorporated herein by reference in its entirety.

Field

The present disclosure relates to a catalytic device for purifying exhaust gas discharged from a gasoline engine.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

Vehicles are necessarily equipped with devices for reducing a variety of harmful substances discharged from engines, and each vehicle includes a device for reducing harmful substances contained in exhaust gas according to combustion methods of the engine of the vehicle.

For example, in a gasoline engine operated by stoichiometric air-fuel ratio control, exhaust gas discharged from the engine is discharged to the air through an exhaust manifold and an exhaust pipe. Harmful substances transferred to the exhaust pipe are reduced while passing through at least one catalytic device, installed to the exhaust pipe, together with exhaust gas.

A WCC (Warm up Catalytic Converter) and a UCC (Under floor Catalytic Converter) are sequentially installed to the exhaust pipe for discharge of exhaust gas discharged from the gasoline engine operated by stoichiometric air-fuel ratio control, and the exhaust gas may be purified by passing through the WCC and the UCC.

Generally, the efficiency of removal of NOx and CO/HC of the WCC and UCC is influenced by a catalyst oxidizing atmosphere using oxygen.

For example, since the WCC and the UCC are activated by heat in an acceleration section, they have high efficiency of removal of NOx in this section. However, when oxygen remains in the WCC and UCC, a portion of NOx may be discharged without being purified. As such, oxygen is the biggest cause for deterioration in efficiency of the WCC and UCC.

Since power is not required during the deceleration of the vehicle, fuel efficiency may be improved when fuel cut is applied to the vehicle. However, we have discovered that since oxygen is stored in the WCC and UCC immediately after the fuel cut, the efficiency of removal of NOx may be lowered.

FIG. 1 illustrates discharge of NOx for each section after fuel cut in a stoichiometric air-fuel ratio gasoline engine.

When fuel cut is performed in section A, fuel is not combusted in the section and NOx is thus not discharged. However, we have discovered that since oxygen is fully stored in OSCs (Oxygen Storage Components) of a WCC and a UCC, NOx purification performance may be deteriorated later.

Then, the fuel cut is completed in an O₂ purge section (section B) and an idling section (section C), and a mixture is combusted in a rich state. However, since the WCC and the UCC are in an oxidizing atmosphere, NOx purification performance may be deteriorated for a certain time.

Meanwhile, a large amount of NOx is discharged to the outside, without being purified by both the WCC and the UCC, in an acceleration section (section D).

As such, since NOx is rapidly discharged immediately after the fuel cut, we have found that there is a limit in improving fuel efficiency by reducing the application of the fuel cut.

SUMMARY

The present disclosure provides a catalytic device for a stoichiometric air-fuel ratio gasoline engine, which is capable of purifying NOx immediately after fuel cut while maintaining the same layout as an existing device in a gasoline engine controlled at a stoichiometric air-fuel ratio, and a catalytic system including the same.

Another form of the present disclosure is directed to a catalytic device for a stoichiometric air-fuel ratio gasoline engine, which is capable of enlarging fuel cut by purifying NOx immediately after the fuel cut so as to improve fuel efficiency while coping with exhaust gas regulations, and a catalytic system including the same.

Other advantages of the present disclosure can be understood by the following description, and become apparent with reference to the forms of the present disclosure. Also, it is obvious to those skilled in the art to which the present disclosure pertains that the objects and advantages of the present disclosure can be realized by the means as described in the present disclosure and combinations thereof.

In accordance with one form of the present disclosure, a catalytic device for a stoichiometric air-fuel ratio gasoline engine, in which exhaust gas discharged from a gasoline engine sequentially passes through a WCC (Warm up Catalytic Converter) and a UCC (Under floor Catalytic Converter), includes an LNT (Lean NOx Trap) component added to at least one of the WCC and the UCC. In particular, the LNT component may include at least one of platinum and barium.

The LNT component may be included in the UCC.

A three-way catalyst may be applied to the WCC.

In another form, a catalytic system including a catalytic device for a stoichiometric air-fuel ratio gasoline engine includes: a gasoline engine in which combustion is controlled at a stoichiometric air-fuel ratio; an exhaust pipe through which exhaust gas is discharged from the engine; a WCC (Warm up Catalytic Converter) installed to the exhaust pipe; a UCC (Under floor Catalytic Converter) installed downstream of the WCC in the exhaust pipe while being spaced apart from the WCC; an oxygen sensor installed in front of the WCC and another oxygen sensor installed between the WCC and the UCC in the exhaust pipe; and an ECU (Electronic Control Unit) configured to receive engine data from the gasoline engine and an output value from the oxygen sensors so as to control the combustion in the gasoline engine. In particular, at least one of the platinum (Pt) and barium (Ba) is added to at least one of the WCC and the UCC.

The platinum or the barium may be added to the UCC.

A three-way catalyst may be applied to the WCC.

Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

FIG. 1 is a typical graph illustrating discharge of NOx for each section after fuel cut in a stoichiometric air-fuel ratio gasoline engine;

FIG. 2 is a diagram schematically illustrating a catalytic device for a stoichiometric air-fuel ratio gasoline engine and a catalytic system including the same according to the present disclosure; and

FIG. 3 is a graph illustrating a NOx reduction effect by the catalytic device for a stoichiometric air-fuel ratio gasoline engine and the catalytic system including the same according to the present disclosure.

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

A catalytic device for a stoichiometric air-fuel ratio gasoline engine and a catalytic system including the same according to the present disclosure will be described below in more detail with reference to the accompanying drawings.

An LNT (Lean NOx Trap) component is added to a catalytic device for a stoichiometric air-fuel ratio gasoline engine in order to remove NOx contained in exhaust gas immediately after fuel cut.

FIG. 2 illustrates that exhaust gas is discharged from an engine 11 through an exhaust pipe 12 to the outside, and a WCC (Warm up Catalytic Converter) 21 and a UCC (Under floor Catalytic Converter) 22 are sequentially installed to the exhaust pipe 12.

The engine 11 is a gasoline engine in which combustion is controlled at a stoichiometric air-fuel ratio, and is connected to the exhaust pipe 12 so that the exhaust gas discharged from the engine 11 passes through the WCC 21 and the UCC 22 in turn.

In this case, the LNT component is added to one of the WCC 21 and the UCC 22.

An LNT is a catalytic device used to purify the exhaust gas from an engine such as a diesel engine in which combustion is controlled in a lean state. The LNT stores NOx in an LNT catalyst when the diesel engine is typically driven (in a lean mode), and then reduces the NOx, which is stored in the LNT catalyst, to N₂ through periodic regeneration (in a rich mode) and discharges the N₂.

Accordingly, the LNT component is added to one of the WCC 21 and the UCC 22, and NOx contained in exhaust gas immediately after fuel cut is stored in the LNT component. Consequently, it is possible to inhibit or prevent a large amount of NOx from being discharged to the air immediately after the fuel cut.

Meanwhile, the LNT component may include at least one of platinum (Pt) and barium (Ba).

Since the LNT component is added to a conventional WCC or UCC, the WCC 21 or UCC 22 may be applied as it is without changing the layout thereof in order to add the LNT component thereto.

Moreover, in one form, the LNT component may be added to the UCC 22 from among the WCC 21 and the UCC 22. Since the temperature of the LNT component desired to occlude NOx is approximately 300° C. to 400° C., the LNT component is added to the UCC 22 rather than the WCC 21 which is immediately adjacent to the engine 11.

Meanwhile, the LNT component is added to the UCC 22 as described above, and a three-way catalyst is applied to the WCC 21.

In an engine such as a diesel engine in which lean combustion is performed, a NOx regeneration process or a desulfurization process is involved to desorb NOx from an LNT. However, in the stoichiometric air-fuel ratio gasoline engine 11, there is no need for a NOx regeneration process or a desulfurization process to remove NOX from the LNT component in the UCC.

This is because the amount of NOx adsorbed to the LNT component immediately after the fuel cut is small, and combustion is controlled in a rich state for O₂ purge immediately after the fuel cut in the stoichiometric air-fuel ratio gasoline engine 11.

In addition, since the temperature of the UCC 22 is approximately 600° C. or more during the acceleration of the vehicle after the fuel cut is performed, there is no need for a separate desulfurization process.

Moreover, the device does not affect hydrocarbon (HC) and carbon monoxide (CO).

Meanwhile, a catalytic system for a stoichiometric air-fuel ratio gasoline engine includes the above-mentioned catalytic device.

As illustrated in FIG. 2, the catalytic system including a catalytic device for a stoichiometric air-fuel ratio gasoline engine includes: a gasoline engine 11 in which combustion is controlled at a stoichiometric air-fuel ratio; an exhaust pipe 12 through which exhaust gas is discharged from the engine 11 to the outside; a WCC (Warm up Catalytic Converter) 21 which is installed to the exhaust pipe 12; a UCC (Under floor Catalytic Converter) 22 which is installed downstream of the WCC 21 in the exhaust pipe 12 while being spaced apart from the WCC 21; at least one oxygen sensor 23 or 24 which is installed in front of or behind the WCC 21 or the UCC 22 in the exhaust pipe 12; and an ECU (Electronic Control Unit) 31 which receives engine data from the gasoline engine 11 and output values from the oxygen sensors 23 and 24 to control the combustion in the gasoline engine 11. Platinum (Pt) or barium (Ba) as an LNT component is added to at least one of the WCC 21 and the UCC 22.

The LNT component is a constituent component of a catalytic device used to purify exhaust gas from an engine such as a diesel engine in which combustion is controlled in a lean state. After NOx is stored in an LNT catalyst when the engine is typically driven (in a lean mode), the NOx stored in the LNT catalyst is reduced to N₂ through periodic regeneration (in a rich mode) so as to discharge the N₂. Thereby, the NOx discharged to the air is reduced.

The LNT component is added to one of the WCC 21 and the UCC 22. In one form, the LNT component may be added to the UCC 22. This is because the temperature of the UCC 22 is in a range of approximately 300° C. to 400° C. at which the LNT component is desired to occlude NOx.

Meanwhile, a three-way catalyst is applied to the WCC 21.

FIG. 2 illustrates an example in which the oxygen sensors 23 and 24 are respectively installed in front of and behind the WCC 21. The ECU 31 controls combustion related to an air-fuel ratio, an ignition timing, and the like in the engine 11, or causes the rich combustion in the engine to be performed for O₂ purge, through the data input from the engine 11 and the oxygen concentrations measured by the oxygen sensors 23 and 24 in front of and behind the WCC 21, thereby reducing exhaust gas. In addition, another oxygen sensor may be installed behind the UCC 22 to measure the oxygen concentration of exhaust gas passing through the UCC 22.

FIG. 3 illustrates an effect by the catalytic device for a stoichiometric air-fuel ratio gasoline engine and the catalytic system including the same according to one form of the present disclosure.

In the present disclosure, the LNT component is added to the UCC 22. Accordingly, even when a large amount of NOx is discharged from the engine 11 immediately after the fuel cut, the NOx discharged from the engine 11 is occluded in the UCC 22 through the above configuration. Therefore, it is possible to reduce an amount of NOx discharged to the outside so as to satisfy exhaust gas regulations.

Meanwhile, the NOx occluded in the UCC 22 immediately after the fuel cut may be removed by injecting rich fuel for O₂ purge in the engine after the fuel cut.

Thus, it is possible to inhibit or prevent a large amount of NOx from being discharged to the air immediately after the fuel cut, and to improve fuel efficiency without increase in exhaust gas since the fuel cut is increased during the driving of the vehicle.

In accordance with a catalytic device for a stoichiometric air-fuel ratio gasoline engine and a catalytic system including the same according to exemplary forms of the present disclosure, an LNT component capable of occluding NOx is added to a catalytic device located at the rear of an exhaust pipe, and NOx can thus be purified by the LNT component, regardless of oxygen storage capacity therein. Therefore, NOx can be purified immediately after fuel cut.

In addition, we have discovered that reduction in the application of the fuel cut can be resolved in order to inhibit or prevent NOx purification performance from deteriorating immediately after the fuel cut. Therefore, NOx can be purified immediately after the fuel cut, and the fuel cut can be enlarged so as to improve fuel efficiency.

Furthermore, since only the LNT component is added to the catalytic device, the catalytic device can be applied to the vehicle without changing the layout thereof while maintain the layout of an existing catalytic device.

While the present disclosure has been described with respect to the specific forms, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A catalytic device for a stoichiometric air-fuel ratio gasoline engine, in which exhaust gas discharged from a gasoline engine sequentially passes through a WCC (Warm up Catalytic Converter) and a UCC (Under floor Catalytic Converter), the catalytic device comprising: an LNT (Lean NOx Trap) component added to at least one of the WCC and the UCC, wherein the LNT component comprises at least one of platinum and barium.
 2. The catalytic device of claim 1, wherein the LNT component is comprised in the UCC.
 3. The catalytic device of claim 2, wherein a three-way catalyst is applied to the WCC.
 4. A catalytic system including a catalytic device for a stoichiometric air-fuel ratio gasoline engine, the catalytic system comprising: a gasoline engine in which combustion is controlled at a stoichiometric air-fuel ratio; an exhaust pipe through which exhaust gas is discharged from the gasoline engine; a WCC (Warm up Catalytic Converter) installed to the exhaust pipe; a UCC (Under floor Catalytic Converter) installed downstream of the WCC in the exhaust pipe while being spaced apart from the WCC; an oxygen sensor installed in front of the WCC and another oxygen sensor installed between the WCC and the UCC in the exhaust pipe; and an ECU (Electronic Control Unit) configured to receive engine data from the gasoline engine and an output value from the oxygen sensors so as to control the combustion in the gasoline engine, wherein at least one of platinum (Pt) and barium (Ba) is added to at least one of the WCC and the UCC.
 5. The catalytic system of claim 4, wherein the at least one of the platinum and the barium is added in the UCC.
 6. The catalytic system of claim 5, wherein a three-way catalyst is applied to the WCC.
 7. The catalytic system of claim 1, wherein the WCC or UCC including the at least one of the platinum (Pt) and barium (Ba) is configured to store nitrogen oxides (NOx) and to reduce the stored NOx to molecular nitrogen (N2) based on a status of the combustion. 